There is considerable prior art in the drafting of yarns, and particularly for polyester yarns. U.S. Pat. No. 3,539,680 discloses one system where speeds disclosed are around 600 meters per minute to 1500 meters per minute; however, relatively speaking, this is a very expensive system requiring equipment and maintenance that we think can be omitted with the system that we propose herein.
Pretensioning yarn in a drafting system before the yarn contacts any heated device, whether such device be a fixed pin, a rotating roll, a stationary contact heater or other type of device, is an important contribution toward obtaining a uniformly dyeable and defect-free yarn. U.S. Pat. No. 3,539,680 mentioned above recognizes the importance of such pretensioning so as to minimize occurrence of "fluffs" and dyeing unevenness (Col. 4, lines 43-47). The patent discusses an arrangement for obtaining such pretension by providing the combination of a nip roller and a delivery roller, and employing a ratio of peripheral speeds of the delivery roller to the heated feed roller within the range of 1:1.001-1:1.030. Thus the patent discloses establishing a pretension zone which is designed to draw the yarn slightly, as indicated by the given ratio range, in order to achieve the required pretensioning. The patent indicates alternatively that a thread brake or guide may be used if it can impart uniform and predetermined tension.
Other types of drafting systems employ heated pins, heated plates, and heated plates with separator rolls, all of which are well known. The quality of the yarn produced on these systems, however, has been found to be generally poor due to the high level of broken filaments and poor dye uniformity than that produced on a system such as represented by the above-mentioned U.S. Pat. No. 3,539,680, and the problems of broken filaments and poor dye uniformity have been found to increase as the speed is increased. Broken filaments tend to cause defects, which cause waste and loss of time.
An object of our invention is to provide a low friction drafting system which provides automatic pretensioning of the yarn before the yarn contacts any heated device and without employing the usual structures upstream from such heated device to provide such pretensioning.
U.S. Pat. No. 3,919,748 discloses an apparatus for altering the length of a synthetic continuous filament or yarn strand. The apparatus comprises a first strand feeding means involving a driven feed roll and a separator idler roll; a first heating means in the form of a heated roll connected to and coaxial with the driven feed roll and having a separator idler roll; a second heating means in the form of a heated plate over which the yarn strand slides; a second feeding means in the form of a driven roller and a separator idler roller; and a driven take-up spool. All of the embodiments in the patent, except one, show the "first heating means", which is the heated roll, as being rigidly connected to the first driven feed roll. The exception is the embodiment shown in FIG. 4 where the "heated roller 20'" turns freely on stud 23 of the swinging arm 26 and thus is turned only by the yarn strand as the yarn strand loops around the heated roller. The patentee does not give any reason for the purpose of this exception nor does he offer any advantages. There is no recognition by the patentee, therefore, that pretensioning of the yarn would automatically occur upstream of the heated roller 20' in the area between the exit of the yarn strand from the driven feed roll 17 (FIG. 4) and the initial contact of the yarn strand with the heated roller 20'. Although FIG. 4 does not illustrate a separator idler roller, it is assumed that it would be positioned as illustrated in FIG. 6. Also, although the patentee does not indicate in his discussion of the embodiment of FIG. 4 that the separator idler roller for heated roller 20' would need to be independently rotatable from the separator idler roller for the driven feed roll 17, it is assumed that this would be desirable. In reference to FIG. 6, therefore, a "thread guide" 37 is provided between the coaxially aligned driven feed roll and heated roller on one side and the separator idler rollers on the other side which serves to displace the yarn strand from the driven feed roll to the heated roller. Since this is probably a high tension zone, this thread guide in the embodiment of FIG. 4 will tend to damage the yarn strand which will lead to the generation of an excessive number of broken filaments in the yarn. The yarn strand filaments which are directly in contact with the surface of the thread guide 37 will be damaged to the extent that they will break in the subsequent drafting of the yarn strand.
Another object of the invention, therefore, is to insure that there is no frictional contact made with the yarn in the area between the exit of the yarn from the input feed roll and the initial contact of the yarn with the freely rotatable heated roll.
Still another object of our invention is to provide a low maintenance drafting system.
A further object of our invention is to provide a drafting system which will operate satisfactorily from a mechanical quality and dye uniformity standpoint, at speeds up to 1500 meters per minute and greater.
A still further object is to provide a less expensive drafting system for providing textile yarns of equivalent quality to those made by the process disclosed in U.S. Pat. No. 3,539,680.